ALGORITHM FOR MOTORISED ACTUATOR

[bmsg]

In one of the process plants for which we are developing the application software, there are electrical (motorised) actuators for continuous control(PID type) of process parameters, like pressure and flow.

The motorised control valves have no position feedback. From the PLC, two numbers of Digital outputs (DO) are available - one for opening the valve & the other for closing it. The 'PID' control is being done in the PLC.

Can anyone suggest in what fashion I may vary the on-time of the pulses from the PLC to carry out PID control of the process parameters?

Incidentally, I am using a 620-35 PLC from Honeywell, for this project.

 

[danw2]

By now you've probably done what needs doing, but the easiest solution is a stand alone PID loop controller, like the Honeywell UDC 3300, configured for "three position step control" (3PST).

3PST uses two output relays to drive the motor CW or CCW, using an "open feedback loop", relying on the consistent timing/stroking of the motor to keep track of the motor position.

3PST was a European innovation, introduced a decade ago to the US. You might find a tech note explaining the algorithm and engineer for the 620 PLC, but frankly, it's a simple task to let a UDC 3300 do it.

Dan